Liquid crystal displays (LCDs) are becoming increasingly prevalent in high-density projection display devices. These conventional high density projection-type color display devices include a light source which emits white light. Dichroic mirrors separate the white light into its corresponding red, green and blue (RGB) bands of light. These color bands of light are then directed toward a corresponding liquid crystal valve which either permits or prevents the light transmission. The RGB bands of light which are permitted to be transmitted through the light valves are then combined by a prism. A projection lens then magnifies and projects the image onto a projection screen.
A conventional liquid plate comprises lens arrays, a lens for collecting white light from a source and dichroic mirrors for separating the white light into red light, green light and blue light. A polarizing beam splitter (PBS) separates the S-polarized-light components of the red, green and blue range. It allows the separated S-polarized-light components of the light to project on reflex crystal plates and a cross dichroic prism for synthesizing the images of P-polarized-light components. The P-polarized-light components are modulated and reflected to be the output. A projection lens projects the image light on a screen.
In the current form of the technology, the production of red light is a problem when utilizing ultra-high pressure (UHP) mercury vapor arc lamps as a light source. There is not a lot of red light emanating from the UHP mercury vapor lamps. Furthermore, it is difficult to insert light from multiple sources into a system without increasing the complexity of the illumination optics. Consequently, the coupling efficiency of the light into the light valve is reduced.
The liquid crystal display device described in U.S. Pat. No. 5,537,171, entitled “Liquid Crystal Projection Display” to Ogino et el., is confined to a liquid crystal panel means, a projection lens means and a screen means that enhances relative corner illuminance without reducing light capturing efficiency. However, the liquid crystal panel means does not produce a lot of red light but rather an orange light.
The liquid crystal projector described in U.S. Pat. No. 6,343,864, entitled “Liquid Crystal Projector Equipment” to Tajiri, is confined to mounting polarizing beams splitters (PBS) in the manner where the PBS transmits more green and blue light than red light. This arrangement produces more orange light than the desired red light.
What is needed is an apparatus that will provide additional red light without reducing the coupling efficiency of the light into the light engine.